Cordless modem system having multiple base and remote stations which are interusable and secure

ABSTRACT

A cordless modem system where a mobile station unit (MSU) is located in the computer and a base station unit (BSU) is connected to the telephone line. A radio frequency (RF) link is developed between the two units to allow a cordless connection. A series of commands are used between the two units to allow the MSU to request a channel, the BSU to grant a channel, the BSU to notify of a ring, and the MSU to request the BSU to go off hook. In addition, there is preferably a command sequence to allow authorization of a particular MSU or BSU. There are two full duplex channels in each MSU and BSU. This allows multiple BSUs and MSUs to be utilized in a small area. Communications between the two units are secure based on address values for each unit contained in the various commands. The communications software utilized in the computer is not even aware of the presence of the cordless connection. Two embodiments of the MSU are provided, one configured as an external data access arrangement (DAA) to be connected with laptop modems configured to utilize external DAAs, and in a second embodiment the MSU is incorporated with the modem hardware to provide a single, fully integrated unit. The BSU is a single preferably relatively small box which simply plugs into the telephone line.

RELATED CASES

This is a continuation of application Ser. No. 08/541,287 filed Oct. 10,1995 now abandoned which is in turn a file wrapper continuation ofapplication Ser. No. 08/242,122 filed on May 13, 1994 abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system having a cordless connection between amodem in a computer and a telephone land line, and more particularly toallowing multiple units and yet maintaining security of each connection.

2. Description of the Related Art

Mobile computers, particularly laptop computers and notebook computershave become increasingly popular. They have performance and capabilitiesnear that of a desktop unit, and if color active matrix liquid crystaldisplays are utilized, the display is as good as a desktop unit. Whencombined with the mobility, the popularity is quite understandable.However, one problem with using portable computers is that often theyneed to be connected to various equipment. For example, when located ina office, it is desirable to connect to various office wide items ornon-portable items. For example, a network interface is often necessary,as is a SCSI port for use with various external devices such as CD-ROMs.This situation has conventionally been handled using expansion bases,which contain expansion cards for network and SCSI use and connectionsfor a video monitor, a printer and a full size keyboard, or portreplicator strips, which are used to simply provide the connections tothe monitor, printer and keyboard without the need for expansion cards.

One of the computer applications which is becoming prevalent iselectronic mail or E-mail. The modem business often has a local areanetwork (LAN), with E-mail and appointment calendar applications. Aremote user, such as the laptop user away from the office needs to checkperiodically to maintain in full contact. Thus, a very common additionto a portable computer is a modem to allow remote access to the LAN orother dial up services. Typically this modem is installed in the laptopcomputer, not directly in any expansion base. So while an expansion baseor port replicator may alleviate certain wiring problems, as the variouscables need not be disconnected or connected when removing or installingthe portable computer, it does not resolve the wiring concerns in thecase of a modem, where a separate telephone line is still required to beplugged and unplugged into the modem in the computer. This results inaggravation for the user. Further, this phone line is yet another of thetangled mass of cables utilized with the modem computer. While themonitor, keyboard and SCSI cables are generally located right next tothe computer to interconnect the various components, the telephone lineoften has to be strung across an office and thus is either unsightly orvery difficult to route. This is a further drawback to standardconventional modem communications where the modem is contained in thepersonal computer, be it a laptop or a desktop unit.

Thus the use of a modem in a laptop computer results in aggravations forthe user and additionally requires unsightly and cumbersome cabling.Therefore it is clearly desirable to simplify both the laptopportability concerns and the unsightly wiring problem.

SUMMARY OF THE PRESENT INVENTION

The present invention relates to a cordless modem system where a mobilestation unit (MSU) is located in the computer or connected to thecomputer and a base station unit (BSU) which is connected to thetelephone line. A radio frequency (RF) link is developed between the twounits to allow a cordless connection between the computer and thetelephone line. The BSU is completely powered from the telephone line,while the MSU is powered from the computer system. A software protocolis utilized between the two units to open a channel when a call isreceived or the computer wishes to go off hook. Each MSU and BSU have apersonalized identification. The BSU is allowed to performcommunications only with authorized and identified MSUs, while the MSUcan perform communications only with BSUs with which it has previouslycommunicated. A series of commands are present between the two units toallow the MSU to request a channel, the BSU to grant a channel, the BSUto notify of a ring, and the MSU to request the BSU to go off hook. Inaddition, there is preferably a command sequence to allow authorizationof a particular MSU for use with the BSU.

Preferably, there are two channels in each MSU and BSU, each channelbeing full duplex. This presence of two channels allows multiple BSUsand MSUs to be utilized in a small area if desired. Once a particularBSU is receiving input or has made a connection with a particular MSU,the BSU is then dedicated to that MSU for the duration of the call. Byhaving two channels, two BSUs can be present in the same environment.Communications between the two units are secure in that the BSUs andMSUs include collision detection logic to determine if both channels arealready active. If so, the MSUs and BSUs do not start communication. Ifa channel is available, an MSU requests that channel, with the requestcommand including the address or identification number of the MSU. TheBSU receives the authorization request, checks its list of authorizedMSUs and if present and the channel is available, provides a grantcommand to the MSU. When the BSU receives a call and a ring from thetelephone line, after checking for an open channel, the BSU transmits adesignated MSU identification along with a ring indication command sothat only the specified MSU will answer the call. Further, the grant andring indication commands include the BSU identification number so thatthe MSU will communicate only with that particular BSU while the call ison-going. In this manner, one MSU will not intercept the calls foranother MSU after the link has been established and a BSU will notprovide calls to unauthorized MSUs. This allows data transfer to besecure even though multiple MSUs are present and can generally share asingle BSU.

Further, the development of the protocol is such that the communicationssoftware utilized in the computer is not even aware of the presence ofthe cordless connection. Both the MSUs and BSUs contain microcomputersand proper signaling to sense what action is requested from the modem ortelephone line and perform the cordless or radio transmission functionseamlessly. Thus conventional communication software can be utilizedwithout any particular special commands or structure. This allows theuser to continue to use his preferred communication software package.

Two embodiments of the MSU are provided, one configured as an externaldata access arrangement (DAA) to be connected with laptop modemsconfigured to utilize external DAAs, while in the second embodiment theMSU is incorporated with the modem hardware to provide a single, fullyintegrated unit. The BSU is a single, preferably relatively small, boxwhich simply plugs into the telephone line.

Thus by having this transparent cordless link, the laptop user does nothave to disconnect or connect a telephone line each time he moves hislaptop and further the telephone line need not be routed across openareas or through difficult passages.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 is a block diagram showing the computer, cordless connection andtelephone jack according to the present invention;

FIG. 2 is a block diagram illustrating multiple computer and MSUs andmultiple BSUs of FIG. 1;

FIG. 3 illustrates the frequencies used by the RF link;

FIG. 4 is a block diagram of the mobile station unit of FIG. 1;

FIG. 5 is a block diagram of the base station unit of FIG. 1;

FIG. 6 is a block diagram of a prior art modem utilizing an externalDAA;

FIGS. 7A and 7B are schematic diagram of the external DAA interface ofFIG. 6;

FIG. 8 is the schematic diagram of the internal DAA of FIG. 6;

FIG. 9 is a block diagram of a combined modem and MSU unit according tothe present invention;

FIG. 9A is a diagram illustrating the installation of the integratedmodem and MSU in a computer;

FIGS. 10A, 10B, 10C, 10D and 10E are flowchart illustrations of theoperation of the mobile station unit of FIG. 1; and

FIGS. 11A, 11B, 11C, 11D and 11E are flowchart illustrations of theoperations of the base station unit of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, the basic arrangement of the componentsaccording to the present invention is shown. A computer system C,preferably a laptop or notebook computer but optionally a desktopcomputer, contains an internal modem M which is connected to a mobilestation unit (MSU) 1. The MSU 1 includes an antenna 400. A telephonewall jack J is connected to telephone land line. A base station unit(BSU) 2 is connected to the telephone jack J and also includes anantenna 402. A radio frequency (RF) link is established between the MSU1 and the BSU 2 to pass information between the computer C and thetelephone jack J. The MSU 1 contains a serialized identification number,preferably 24 bits long, as does the BSU 2. This allows the MSU 1 tohave a unique identity to allow security of communications. Similarly,the BSU 2 also has this identification to allow a secure link to beestablished. The MSU 1 is connected to the internal modem M by severalalternate connections. In a first embodiment the MSU 1 is configured asan external data access arrangement (DAA) and is connected to anexternal DAA port of the internal modem M. In this embodiment the MSU 1is contained in a small box or case. In an alternate embodiment the MSU1 and the internal modem M are combined into a single unit, preferablyin a PCMCIA form factor. The BSU 2 is connected only to the telephonejack J and is not otherwise powered but receives power from thetelephone line. The BSU 2 is contained in a small box or case. Thedetails of the MSU 1 and the BSU 2 are provided below.

The RF link between the MSU 1 and the BSU 2 is a two channel, fullduplex link as illustrated in FIG. 3. Center frequencies of 35.2 MHz and43.24 MHz are preferably utilized with each channel. Each channel isdeveloped as a five kHz sideband of the basic carrier, so that eachchannel has a 10 kHz bandwidth. The 35.2 MHz frequency is used as thetransmit channel from the BSU 2 to the MSU 1, while the 43.24 MHzfrequency is used as being receive channel from the MSU 1 to the BSU 2.The separation of frequencies allows both for duplex operation and alsomeans that the MSU's 1 are not capable of receiving signals beingtransmitted by other MSU's, so that security is enhanced. The securityprocess is described in more detail below.

Referring now to FIG. 2, a more complex arrangement is shown. In thiscase three computers C1, C2 and C3 include respectively MSUs 1, 1′ and1″. In addition, there are two telephone jacks J1 and J2 receivingrespectively BSU 2 and BSU 2′. The two BSU 2 and BSU 2′ are within thesignal range of each other, so that if they were to utilize the samechannel interference would occur. However, because two differentchannels are utilized, two BSUs can communicate within the same generalarea. Each MSU 1, MSU 1′ and MSU 1″ is free to communicate with eitherBSU 2 or BSU 2′ depending upon channel availability and authorizationaccess of the particular BSU 2 and BSU 2′.

Referring now to FIG. 4, the block diagram of the MSU 1 is shown. An RJ45 connector 404 is provided in the MSU 1 to allow connection of a cablebetween the MSU and the internal model M. A modem interface 406 isconnected to the RJ 45 connector 404 and interfaces with the varioussignals. A power supply 408 is provided and connected to the modeminterface 406 to receive power from the computer C and to provide theproper voltages for operation of the MSU 1. DAA identifier logic 410 isconnected to the modem interface 406 to identify that the MSU 1 isconnected to the internal modem M. A microcontroller 412, preferably the68HC05 from Motorola, operates as the control point for the MSU 1. ADTMF decoder/encoder 414 is provided to allow signaling and dialing ifnecessary. An RF transmitter 416 is connected to properly frequencymodulate the received audio signal and provide it to an antenna 418. Thetransmitter 416 is controlled by the microcontroller 412. A receiver 420is connected to the microcontroller 412 and the antenna 418 to receivethe RF signal from the base station BSU 2 and provide the audio signalto the modem interface 406. The receiver 420 is similarly controlled bythe microcontroller 412.

Now the connections between the blocks will be described in more detail.The modem interface 406 receives the MODEM_CLK signal from the RJ 45connector 404 and inverts and buffers this signal to develop a˜MODEM_CLK signal provided to the DAA identifier logic 410. In thisdescription a tilde prefix or an asterisk suffix is used to indicate anegative logic signal which is active when asserted low. The signal namewithout the tilde or asterisk means that it is the inverse of thatsignal with the tilde or asterisk. Similarly, the modem interface 406receives the ˜DTAL or inverted data signal from the DAA identifiercircuitry 410 and provides a buffered and inverted version to the RJ 45connector 404. The DAA identifier logic 410 is configured to provide acode to the internal modem M to indicate the presence of the MSU 1should the internal modem M need to make any changes. Conventionally theDAA identifier logic 410 provides the country code of the particularcountry for which the mobile station MSU 1 and base station BSU 2 areconfigured for operation. In an alternate embodiment the MODEM_CLKsignal could be provided to the microcontroller 412, which would thenprovide the DTAL signal. This embodiment slightly complicates theprogramming but also reduces the cost and space by allowing removal ofthe separate DAA identifier logic 410.

An RIL* or inverted ring indication signal is provided from the modeminterface 406 to the RJ 45 connector 404, which in this case is simply abuffered version of the to be ˜RING_IND or ring indication signalprovided by the microcontroller 412. The OH* or inverted off hook signalfrom the RJ 45 connector 404 is inverted and provided to themicrocontroller 412 to indicate that the internal modem M has requestedthe telephone line to go off hook. The TXA and RXAC or transmit analogand receive analog signals from the RJ 45 connector are provided to themodem interface 406. The TXA signal is combined with signals referred toas FSK_TX and DTMF_TX or frequency shift keyed and DTMF transmit signalsby an operational amplifier circuit to develop the AUDIO_TX signal whichis provided to the transmitter 416. Preferably the mobile station MSU 1can provide either the analog or audio data being received from theinternal modem M, which is utilized for conventional datacommunications, or can provide an FSK signal, which is utilized forcommand operations with the BSU 2. The FSK_TX signal is a bufferedsignal provided from a serial output of the microcontroller 412.Preferably DTMF tones can also be provided when necessary. An ˜AUDIO_ENor audio enable signal from the microcontroller 412 is associated withthe AUDIO_TX signal in that it clamps the TXA signal being provided to alow level so that the FSK_TX signal used in the command phase isunimpaired. An AUDIO_RX signal received from the receiver 420, which isthe audio or analog data received over the RF link, is provided in abuffered format to the RXAC output. The ˜AUDIO_EN signal also acts toclamp the AUDIO_RX signal to a low level. Additionally, the RJ 45connector 404 provides ground and 5 volt connections to the modeminterface 406. The modem interface 406 passes the 5 volt and groundconnections to the power supply 408.

The power supply 408 provides a 3 volt output for operation of thecircuitry of the preferred embodiment, to save power, and providesVCC_TX and VCC_RX signals which provide power to the transmitter 416 andthe receiver 420 so that they can be completely powered down when not inoperation. To the end, the VCC_TX_EN and VCC_RX_EN signals are receivedfrom the microcontroller 412 to control or enable the VCC_TX and VCC_RXoutputs. The power supply 408 also provides the ˜RESET signal to themicrocontroller 412 to reset the operation of the MSU 1 when the powersupply is inadequate.

The DTMF decoder/encoder 414 provides the DTMF_TX output, which is usedif dial tones are desired, and receives the AUDIO_RX signal from thereceiver 420 to allow decoding of any received DTMF signals. The DTMFdecoder/encoder 414 is connected to the microcontroller 412 through dataand control signals so that the decoder/encoder 414 can interrupt themicrocontroller when a detected DTMF code is received and can provide abi-directional data and control port.

The transmitter 416 includes a radio frequency phased-locked loop (PLL)synthesizer (not shown) which includes a serial interface. The PLLreceives command and setup data from a serial data link comprised of thesignals MOSI, MISO and SCK from the microcontroller 412. The SCK signalis the clock signal while the other two signals are for the data inputand data output. The serial interface allows the microcontroller 412 toproperly program the PLL contained in the transmitter 416 to the desiredfrequency of channel 1 or channel 2. The output of the PLL is thenprovided to appropriate mixing circuitry to mix in the AUDIO_TX signalto produce the RF_TX signal, which is provided to the antenna 418. Theantenna 418 can either be an integrated antenna or a short externalantenna. Additionally, the microcontroller 412 provides the TX_RF_EN andTX_PLL_EN signals to the transmitter 416. The TX_PLL_EN signal is usedto enable or disable the PLL when desired, while the TX_RF_EN signaldisables the actual output of the transmitter 416 which is provided tothe antenna 418. This allows the PLL to be activated or turned on inpreparation for a transmission which is to occur.

Similarly, the receiver 420 includes a similar PLL, preferably theMC145170 from Motorola Semiconductor. The receiver 420 includes theMOSI, MISO and SCK signals. The transmitter 416 receives the VCC_RXsignal from the power supply 408 to allow it to be completely powereddown. An RX_PLL_EN signal is provided from the microcontroller 412 toreceiver 420 to disable the PLL in the receiver 420. The receiver 420also includes a mixer FM IF system, preferably the NE/SA606 fromPhillips Semiconductor. The mixer FM IF system receives an RF_RX signalfrom the antenna 418 and properly mixes out the channel receivefrequency so that only the received audio data is present. This isprovided as the AUDIO_RX signal to the DTMF decoder/encoder 414 and themodem interface 406. An FSK_RX signal is a buffered version of theAUDIO_RX signal and is provided to a serial input of the microcontroller412. Thus the FSK_TX and FSK_RX signals are serial output and input ofthe microcontroller 412. This serial interface of the microcontroller412 is the command interface with the BSU 2. Preferably the serialinterface operates at a low speed, such as 1200 or 2400 baud. Thereceiver 420 also provides an RSSI or receive signal strength indicationto the microcontroller 412 to indicate that the carrier is beingreceived from a BSU 2 and that a channel is active. This allows the MSU1 to monitor for a received signal indicating that a given channel isbusy.

Thus the MSU 1 provides the capability to receive analog audio data fromthe computer C and provide it over an FM modulated RF link to the basestation BSU 2 and to similarly receive an RF signal from the basestation BSU 2 and decode the signal to provide the RXAC analog signal tothe computer C. The microcontroller 412 provides the control functionwhich is needed for the modem interface and allows command passingbetween the base station BSU 2 and MSU 1.

Referring now to FIG. 5, a block diagram of the BSU 2 is shown. As canbe seen, the organization is very similar to that of the mobile stationMSU 1 except that the modem interface 406 has been replaced by a DAA422. An RJ11 connector 424 is provided to connect the DAA 422 to thephone line. The DAA 422 is connected to a transmitter 426, a receiver428, a microcontroller 430, a DTMF decoder/encoder 432 and a powersupply 434. The DTMF decoder/encoder 432, the transmitter 426 and thereceiver 428 are configured in the fashion similar to that of the mobilestation MSU 1 and will not be further described in detail. Again, themicrocontroller 430 is similar, preferably an M68HC05. The DAA 422contains the necessary interface between the telephone line TIP and RINGsignals which it receives as inputs and the various other signals in thebase station BSU 2. The TIP and RING signals are provided to the powersupply 434 to allow the base station BSU 2 to be entirely powered by thetelephone line. For more details on this technique, please refer tocopending application Ser. No. 08/242,314, filed concurrently herewithissued U.S. Patent No. 5,553,138 on Sep. 3, 1996 and titled “TELEPHONELINE SOURCED POWER SUPPLY,” which is hereby incorporated by reference.The power supply 434 provides the desired 3 volt signal and transmitterand receiver voltages as necessary. The DAA 422 includes a two wire tofour wire conversion to develop the RX signal and utilize the TX signalas is conventionally known. Details of this conversion are not includedbut an example is illustrated in U.S. Pat. No. 5,127,046, which ishereby incorporated by reference. Similarly, in the DAA 422, the FSK_TXand DTMF_TX signals are utilized and combined with the audio signalreceived from two to four wire converter to provide the AUDIO_TX signal.The ˜AUDIO_EN signal is used to clamp or disable the audio signal fromthe two to four wire converter and AUDIO_RX signals so that themicrocontroller 430 can properly communicate with the MSU 1. A RING_INDsignal provided from the DAA 422 to the microcontroller 430 provides aring detection indication which can be transmitted via a command to theMSU 1. The ˜OFF_HOOK signal is provided from the power supply 434 to theDAA 422 and is a combination of a VCC_TX_EN signal and a signalindicating that the power supply 434 needs recharged. Basically thepower supply 434 includes a very large capacitor which is utilized topower the BSU 2 and the capacitor needs periodic recharging from the DCvoltage present on the telephone line. When recharging is necessary, thepower supply 434 causes the BSU 2 to momentarily go off hook to chargethe capacitor. Thus, the ˜OFF_HOOK signal is developed either by thepower supply 434 for charging or by the microcontroller 430 whencommunications are desired based on the VCC_TX_EN signal. In otherrespects the operation and configuration of the BSU 2 is the same as themobile station MSU 1 and details are not provided.

Referring now to FIGS. 6, 7A, 7B and 8, these are block diagrams andschematics of a prior art modem which is located internal to a laptopcomputer and includes provisions for an external DAA. This modem is usedin the preferred embodiment as the MSU 1 of FIG. 4 is designed to workwith the external DAA connection. The modem 12 of FIG. 6 has apreference to use a device connected to the external DAA connectionprior to using the internal DAA, so that if the MSU 1 is present, itwill be utilized rather than the landline interface present on the modem12. This description is provided for full enablement and to allow betterunderstanding of the connections and operation of the mobile stationunit MSU 1.

FIG. 6 shows a logical block diagram of the various elements of themodem 12. The modem 12 preferably consists of two circuit boardscombined to form the small unit which can be contained in a laptopcomputer. A motherboard MO contains all of the components, including anRF11 type jack 14 and an RJ45 type jack 16, except those forming theinternal DAA. The components of the internal DAA are located on adaughterboard DA which overlies the motherboard MO. This allows easysubstitution of internal DAA's for various countries without requiringcomplete design of the entire modem 12, particularly the motherboard MO.The laptop computer physically contains the modem 12 and connects via aninternal connector to a UART/support chip 100. The UART/support chip 100typically connects to the host bus of the laptop computer, for examplean EISA or ISA bus or PCMCIA interface, although it could be any type oftypical communications bus. The UART/support chip 100 then appears as auniversal asynchronous receiver transmitter (UART) to the laptopcomputer. The UART/support chip 100 connects to, among other things, amicrocontroller 102 by both serial and parallel buses. The UART/supportchip 100 provides a variety of functions to the modem 12, includingcommunications to the laptop computer, clock controls, configurableregisters, and power down control for the microcontroller 102. TheUART/support chip 100 is typically an application specific integratedcircuit, but could instead be constructed of discrete components.

The microcontroller 102 is typically an embedded controller, and in thepreferred embodiment is a 68302 integrated multiprotocol processor,manufactured by Motorola Incorporated. A read only memory (ROM) 101 andrandom access memory (RAM) and non-volatile RAM (NVRAM) 103 are providedto allow for sufficient ROM and RAM space to contain the necessaryfirmware and data to operate the modem 12.

The microcontroller 102 communicates with a data pump 104 by both serialand parallel buses. The data pump 104 is typically a modem data pumpchip set supporting the various protocols of modem communication,including V.32bis protocol and fax protocols. In the preferredembodiment, the data pump 104 is a WE® DSP16A-V32FB-LT V.32bis plus FAXData Pump Chip Set, sold by AT&T Microelectronics, and configured for14.4 Kbps operation as a fax/modem. This chip set includes a digitalsignal processor (DSP) support chip 106, a DSP 108, and a coder-decoder(CODEC) 110. This chip set is interconnected according to AT&Tspecifications and provides the typical data pump features of control,analog-digital and digital-analog conversion, digital signal processing,and interfacing.

The microcontroller 102 communicates with the data pump 104 by bothserial and parallel buses. The serial bus is used to transmit andreceive data that will become the transmitted and received modem data,while the parallel bus is used to control and configure various featureswithin the data pump 104. These features are controlled through the DSPsupport chip 106. The data pump 104 converts the digital serial dataprovided by the microcontroller 102 into the appropriate analog format.This is typically done by the DSP 108, which then transmits and receivesthe data via the CODEC 110.

The CODEC 112 connects to the actual external lines through analogtransmit and receive signals, TXA and RXAC. These signals areselectively connected to either an internal DAA 112 or acellular/external DAA interface 114. Details are provided below. Theinternal DAA is then connected to a telephone line by the RJ11 type jack14, while the cellular/external DAA interface 114 can be connectedthrough the RJ45 type jack 16 to an external DAA, a cellular phone or tothe MSU 1.

Various signals are typically used to interface with telephone lines,including the ring indicator signal RI* and the off hook control signalOH*. A DAA generates and receives these signals, as well as the TXA andRXA signals, and converts them into a format suitable for thatparticular country's two-wire telephone system, or whatever type oftelephone system to which the DAA is connected. The internal DAA 112 andthe cellular/external DAA interface 114 receive OH* from the DSP supportchip 106. Three lines are bi-directionally connected to thecellular/external DAA interface 114 and to the internal DAA 112. Theyare the lines carrying the RI* signal, a data signal DTA, and a clocksignal CLK*. The functions of these signals in the modem 12 will becomeapparent.

The microcontroller 102 determines what is externally connected to thejacks and selects whether to use the cellular/external DAA interface 114or the internal DAA 112. The microcontroller 102 further selects whetherto use the cellular/external DAA interface 114 in a cellular phone modeor an external DAA mode. This is all done via the RI* signal, the DTAsignal, and the CLK* signal, and the circuitry to accomplish this willbe shown and described later.

The microcontroller 102 uses the parallel bus between it and theUART/support chip 100 to configure and determine the status of theUART/support chip 100. The UART/support chip 100 includes a number ofregisters addressable by the microcontroller 102. The registers providefor control of and access to a number of digital input/output (I/O) pinson the UART/support chip 100. One register provides the direction ofeach pin, either input or output. Another register provides the datavalue of bits which are set as outputs during a write operation and alldata values when read. Additional bits can select the output pins asbeing tri-stated. Yet another register can select the various pins ascausing an input to the microcontroller 102 upon a transition.

The laptop computer sends and receives data to the modem 12 via theUART/support chip 100, which then serially communicates that data to themicrocontroller 102. The microcontroller 102 then establishes acommunications link through either the internal DAA 112 or thecellular/external DAA interface 114, whichever is selected. To establishthe communications link, the microcontroller 102 directs the propersequence of signals to either originate or answer a telephone call. Forexample, in the land line model, the microcontroller 102 typicallydirects the DSP support chip 106 to drive the OH* signal low, then,after configuring the data pump 104 through their parallel bus,“listens” for a dial tone on the line, and then directs the data pump104 to dial the number. Then, the microcontroller “listens” for ananswer carrier through the data pump 104, and then directs the data pump104 to establish whatever type of data communications link is desired.For the cellular phone 22, the sequence will be cellular specific, butthe principles of establishing a data communications link are the same.

After establishing a data communications link, the microcontroller 102serially sends to the data pump 104 the data to be transmitted to thecommunications device. The data pump 104 then processes this serialdigital data and converts into an analog form suitable for communicationat the rate and in the protocol desired. It then transmits thisinformation via the TXA signal to the device the microcontroller 102 hasselected, the cellular/external DAA interface 114 or the internal DAA112, which then communicates via the active jack. Similarly, receiveddata is transmitted from the active jack through the cellular/externalDAA interface 114 or the internal DAA 112 to the data pump 104, whichsubsequently transmits that data to the microcontroller 102, which thentransmits the data to the laptop computer by way of the UART/supportchip 100. Of course, the microcontroller 102 may performcompression/decompression functions on the data going either direction,or otherwise “massage” the data.

FIGS. 7A and 7B show the circuitry for selecting between utilizing theRJ45 type jack 16 and the RJ11 type jack 14. This selection circuitryselects between the RJ45 type jack 16 shown in FIGS. 7A and 7B, and aninternal DAA connector 200, which then connects to the RJ11 type jack 14via the internal DAA 112, as will be shown later in FIG. 8. Thisselection is accomplished by an internal selection signal INTERNAL,which is provided by the microcontroller 102. The inverse of thissignal, INTERNAL*, is generated by a MOSFET 202 in an invertingconfiguration. In the preferred embodiment, the MOSFET 202 is a 2N7002.When INTERNAL is true, the internal DAA connector 200 is active. WhenINTERNAL is false, then INTERNAL* is true, and the RJ45 type jack 16 isselected for communications.

This selection process is accomplished by activation and deactivation ofCMOS switches, preferably provided in CD4016 devices. Specifically, whenINTERNAL is low, INTERNAL* is high, and the RJ45 type jack 16 isconnected by CMOS switches to the various signal lines required forcommunications with the data pump 104, the UART/support chip 100, andthe microcontroller 102 and the internal DAA connector 200 hasconnections removed from those signal lines by other CMOS switches. TheTXA signal is connected to the RJ45 type jack 16 TXAL signal line via aswitch 204. Similarly, the RXA signal is connected to the RJ45 type jack16 RXAL signal line via a switch 206, the RI* signal is connected to theRJ45 type jack 16 RIL* signal line via a switch 208, and the DTA signalis connected to the RJ45 type jack 16 DTAL signal line via a switch 210.Note that a separate data signal DTAI is also provided for connection tothe signal line DTAL. This is for separate control by themicrocontroller 102, and is simply provided in the preferred embodimentto allow for independent control by the microcontroller 102 of the RJ45type jack 16 DTAL line when the switch 210 is turned off.

When INTERNAL goes high, the internal DAA connector 200 becomes active.The TXA line is then connected to the internal DAA connector 200 TXA0signal line via a switch 212, the RXA line is connected to the RXA0signal line via a switch 214, the RI* signal is connected to the RI0*signal line via a switch 216, and the DTA signal is connected to theDTA0 signal line via a switch 218.

The CLK* signal remains connected to both the RJ45 type jack 16 and theinternal DAA connector 200 at all times. The CLK* signal can be usedbi-directionally by both the microcontroller 102 and the UART/supportchip 100. It is typically, however, used as an input when using aMotorola or Nokia cellular phone, or when using the internal DAA 112 andit is on hook. CLK* is typically used as an output when using either DAAand they are off hook, or when using the external DAA 24 and it is onhook. The OH* signal is provided to the RJ45 type jack 16 as the OH*Lsignal line.

Also connected to the RJ45 type jack 16 are the ground signal GNDL andthe 5 volt power supply +5 VL. All of the signals on the RJ45 type jack16 are protected and isolated by clamping diodes or transorbs 220 andinductors 222. The 5 volt power supply +5 VL is selectively provided tothe RJ45 type jack 16 when the signal DAAPWR* goes true, or low. WhenDAAPWR* goes low, it turns on RJ45 type jack power supply enablecircuitry 224, which then drives +5V to the RJ45 type jack 16 +5 VL linevia the inductor 222.

Before connecting to the RJ45 type jack 16 or the internal DAA connector200, the TXA signal is filtered and driven. Specifically, the TXA signalis coupled through a capacitor 226, a resistor 228, and another resistor230. A gain reduction block can be added if desired. It is then driveninto a low pass filter 232, whose cutoff frequency is well above thehighest frequency needed for modem communications. Here, that cutofffrequency is approximately 42 kHz. The signal is then transmittedthrough a resistor 234, the switch 204, and a coupling capacitor 236.After the coupling capacitor 236, the line can also be sensed orselectively pulled up or down via the signal LCS, connected via aresistor 238. The signal LCS, as well as signals EARTH* and DAAPWR areconnected to the digital I/O pins of the UART/support chip 100 to allowthe microcontroller 102 to control or monitor these signals. The PB1,PB1O, and INTPWR* signals are supplied by the microcontroller 102. Thesesignals are provided for compatibility with international and nationalstandards, for implementation of protocols used by the modem 12, and forcontrol of the cellular phone. Further, PB10 provides themicrocontroller 102 with direct control of the RI* signal.

Similarly, the RXAL signal, before being transmitted to the data pump104, is received from the RJ45 type jack 16, and driven through theinductor 222 and a coupling capacitor 240. It is then selectively driventhrough the switch 206, and is then provided to other circuitry in themodem 12 as the RXA signal. As the data pump 104 requires coupling ofthe RXA signal, the CODEC 110 of the data pump 104 is provided with anRXAC signal, which is generated by coupling the RXA signal in a coupler242.

When the internal DAA connector 200 is selected by the switches 212 and214, the TXA0 signal is first filtered through a capacitor 244 beforebeing driven externally. This capacitor 244 is connected to the switch212. The RXA0 signal is also first filtered through a capacitor 246before being driven through the switch 214. The previously mentionedsignal LCS, in addition to providing a sense and a selectable pullup/pull down to the TXAL signal, also senses or selectively pulls up ordown the TXA0 signal between the internal connector 200 and thecapacitor 244 via a resistor 248. The EARTH* signal also provides asense or selectable pull up/pull down of the RXAL signal between theRJ45 type jack 16 and the capacitor 240 via a resistor 250 and providesa sense or selectable pull up/pull down of the RXA0 signal between theinternal DAA connector 200 and the capacitor 246 via a resistor 252. ThePB10 signal provides a sense or selectable pull up or down of the RIL*line via a resistor 254, and the PB1 signal is used to selectivelyattenuate the TXA signal via a resistor 256, a capacitor 258, and aswitch 259, after that signal has been filtered through the capacitors226 and 228. The DTAL and CLKL signals are pulled up to 5 volts through,respectively, resistors 260 and 262. On the internal DAA connector 200,two additional signals are provided. These are the internal power selectsignal INTPWR*, which is also pulled up by a resistor 264, and the REFsignal, which is a 2.5 volt precision reference.

FIG. 8 shows circuitry associated with the internal DAA 112 and providesan example of the DAA identifier circuitry 410 in the MSU 1. Three mainblocks of circuitry are shown: the country or DAA identificationcircuitry 300, the power down circuitry 302, and the DAA circuitry 304.This circuitry is typically all placed on one board that is thenconnected to the main board of the modem 12 by connectors 305 and 306,which connect to the internal DAA connector 200. This allows forconvenient swapping of internal DAA's when one desires to move to orremain in a different country. As previously discussed, the RJ11 typejack 14 is typically located on the main board of the modem 12, and theconnector 305 allows lines from the DAA circuitry 304 to connect to theRJ11 type jack 14. Typically, the connectors 305 and 306 are separatephysical connectors.

The DAA circuitry 304 is typical DAA circuitry used to connect a modemto a land line, or physical telephone line, and uses the standardsignals TIP, RING, TIPV, RINGV, and GRNDSTRT. The internal DAA 112 isconnected to the internal DAA connector 200 via the connector 306. Allof the signals from the connector 306 connect to the DAA circuitry 304.The signals INTPWR* and the +5V power line connect to the power downcircuitry 302. When INTPWR* goes low, the power down circuitry 302 isenabled, and power is supplied to the DAA circuitry 304 through thesignal INTDAAPWR. Specifically, a power switch 307 is connected to the+5V signal and to the signal INTPWR*. INTPWR* going low turns the powerswitch 307 on, providing power to an inductor 309 that then providespower to the DAA circuitry 304. Filtering the supplied power, andconnected between the inductor 309 and ground, is a filtering capacitor311. The power down circuitry 302 is standard switching circuitry, andis well known to those in electronic design.

The country identification circuitry 300 includes a shift register 308,which in the preferred embodiment is a 74HC165. The shift register 308has certain of its parallel inputs pulled up by pullup resistors 310 andcertain of its parallel inputs pulled down by pulldown resistors 312 toindicate a particular country. The output QH of the shift register 308is driven to its serial input Sl as well as to an output buffer 314. Theoutput buffer 314 is typically a 74HC126, and its output selectivelydrives the data line, DTA0. The LD*/SHF signal input of the shiftregister 308 is driven by an RC circuit consisting of a resistor 316 anda capacitor 318. The resistor 316 is connected to the CLKL signal and tothe capacitor 318, which is then connected to ground. The LD*/SHF signalinput of the shift register 308 is connected between the resistor 316and the capacitor 318. This signal is also connected to the enable lineof the output buffer 314.

When the LD*/SHF signal is high, the output buffer 314 is enabled, andthe shift register 308 serially outputs the contents of its parallelinputs on its QH output as clocked by its CLK signal input, which isconnected to CLKL.

The time constant of the RC filter made up of the resistor 316 and thecapacitor 318 is approximately 0.5 milliseconds. When the clock isrunning at its slow rate, which has a period of much greater than 0.5milliseconds, the LD*/SHF signal remains low, as does the enable line tothe output buffer 314. This instructs the shift register 308 to load itsparallel inputs A through H as specified by the pull up resistors 310and the pull down resistors 312, and tristates the output buffer 314.When the CLKL signal is sped up, the LD*/SHF signal goes high, enablingthe buffer 314 and causing the shift register 300 to shift data on therising edges of the CLKL signal.

The pull up resistors 310 and the pull down resistors 312 are connectedin an arbitrary way to indicate which country's telephone lines the DAAcircuitry 304 is constructed to communicate with. In FIG. 8, the A, B,C, and D lines of the shift register 308 are pulled up, and the E, F, G,and H lines are pulled down. When clocked out, they serially clock outas “00001111.” For another country, another arbitrary value is used.Further, all eight bits need not be used to designate country codes. Forexample, they can designate a type of DAA such as the MSU 1, or aparticular configuration.

In this way, the microcontroller 102 can determine the configuration ofthe internal DAA 112 by “twiddling” the CLK signal and then reading theDTA0 signal returned, which is returned to the microcontroller 102 asthe DTA signal. This circuitry is repeated on any attached external DAA24 in a similar manner. In addition, all eight bits need not be used forcountry encoding but can also be used for other decoding purposes.

The microcontroller 102, through its signal lines INTERNAL and signallines INTPWR* and DAAPWR* can both select and power up and down both theinternal DAA 112 and any external DAA 24. The INTERNAL line allows forselection between the RJ45 type jack 16 and the internal connector 200,while the INTPWR* and DAAPWR* signals respectively provide for poweringup or down the internal DAA 112 or any external DAA 24. The powering upand down of the internal versus the external DAA's is important on alaptop or notebook computer, as keeping these DAA's powered up requiresa good deal of energy. Thus, by powering down these DAA's when they arenot required, the laptop computer that uses the modem 12 can experiencesignificantly increased battery life because of these power savingfeatures of the modem 12.

FIG. 9 shows the block diagram of an alternate arrangement where the MSU1 is integrated with the internal modem M preferably on a single PCMCIAtype II form factor card. In this embodiment the modem M′ does notinclude an RJ11 connector 14 but rather only includes a dual keyed RJ45connector 16 which is connected to the external DAA interface 114. It isnoted that the cellular connection is preferably disabled though itcould optionally be utilized. Preferably also no internal DAA 112 ispresent for space reasons, instead utilizing an external DAA to a landline for direct wired communications. The internal DAA 112 has beenreplaced by the transmitter 416, receiver 420 and antenna 418 of the MSU1. A separate microcontroller 412 is not necessary as themicrocontroller 102 of the modem 12 is capable of performing the samefunctions and can be readily programmed. This allows savings of cost andspace. Further, the DTMF and FSK generation circuitry and signals arenot necessary as this can be provided by the data pump 104 to furthersave space and cost. Thus, the microcontroller 102 is connected to thetransmitter/receiver/antenna unit only with the various enable signals,the serial interface necessary for the PLLs and the RSSI signal.

This physical embodiment is shown in FIG. 9A. The extension on a PCMCIAcard 502 is utilized to incorporate the RF electromagnetics and theantenna 418. The notebook computer M of FIG. 9 includes a PCMCIA slot500 and the modem/MSU 1 M′ is contained in the PCMCIA card 502 which isproperly inserted into the PCMCIA slot 500. Thus in this embodiment theMSU 1 is not contained in a separate box but is simply fully integratedalong with the modem on a single card. An external DAA is necessary fordirect landline operations, but this is acceptable as the primaryconnection to the laptop will be through the cordless link.

As noted above, both the MSU 1 and the BSU 2 contain microcontrollersand as a result software is utilized to control their operation. FIGS.10A-10E and FIGS. 11A-11E illustrate the operation of the microcomputers 412 and 430.

Referring now to FIG. 10A, the MSU 1 commences the BOOT sequence 1000 atstep 1002 where the various inputs of the microcontroller 412 areproperly programmed and the serial control interface with the FSK_RX andFSK_TX signals is initialized. Various tables are read to initialize themicrocontroller 412 and the transmitter 416 and receiver 420 are turnedto an off position, as indicated by the RADIO=OFF variable. This is doneby disabling or negating the TX_RF_EN, TX_PLL_EN, RX_PLL_EN, VCC_TX_ENand VCC_RX_EN signals, so that they are fully disabled and unpowered.Control then proceeds to step 1004, which is the first step in theMSU_MAIN sequence 1100, where the serial control interface for the FSKdata is enabled to allow reception of command data from the BSU 2.Additionally, the receiver 420 is powered and activated or enabled toallow reception of command data from the base station BSU 2. Controlthen proceeds to step 1006, where the PLL in the receiver 420 isproperly set and a dwell timer is set to a preferred value of 330 msecto allow checking of both channels. Control then proceeds to step 1008to determine if the OFF_HOOK signal has been received from the RJ45connector 404. If so, control proceeds to an MSU_CCA sequence 1010. Ifthe OFF_HOOK signal has not been received, control proceeds to step 1012to determine if a ring indication command has been received from theserial control interface. This would indicate that the BSU 2 hasprovided a ring indication command to the MSU 1 to indicate the presenceof an incoming call that needs to be answered. The format of the variouscommands is shown in Table 1 at the end of this description. If an RI ispresent, control proceeds to the MSU_RING sequence 1014.

If an RI was not received, control proceeds to step 1014 to determine ifthe dwell time has elapsed. If not, control returns to step 1008 tocontinue scanning this channel for an off hook or ring indication. Ifthe dwell time has elapsed, it is time to proceed to the next channel.Control proceeds to step 1016 where the channel is changed. Thepreferred embodiment utilizes two channels for simplicity, but a greaternumber of channels could be utilized. After incrementing the channel,control proceeds to step 1006 to continue to wait for either an off hookor ring indication command.

The MSU_CCA sequence 1010 (FIG. 10B) commences at step 1020 where afirst channel is selected and a channel vacant timer is set. Preferablythis time is 150 msec. This time is used to determine if another MSU 1is operating on the same channel. Control then proceeds to step 1022 todetermine if the RSSI signal is being received from the receiver 420. Ifnot, control proceeds to step 1024 to determine if the channel vacanttime has terminated. If not, control returns to step 1020 to determineif the channel is active and being utilized. If the channel vacant timehas completed, control proceeds to the AG_SCAN sequence 1026. Thus theloop first checks for a currently occupied channel to avoid disruptingoperations of the session in progress and to provide security. If theRSSI signal is asserted in step 1022, control proceeds to step 1028where the channel vacant timer is cleared and then to step 1030 to againdetermine if the RSSI signal is still asserted. If not, control returnsto step 1022 as the channel was just vacated. If it is still asserted,control proceeds to step 1032 to determine if the channel vacant timerhas completed. If not, control returns to step 1030. Thus, if at anytime during the channel vacant search time the channel clears, thechannel vacant time is restarted so that a channel must be clear for atleast 130 msec before a MSU 1 attempts to contact the base station BSU2. If the time value has been completed, control proceeds from step 1032to step 1034, which is also the entry point of the CHANGE_CH sequence1036. In step 1034 the channel number is incremented and rolled over tothe next channel if necessary. Control then proceeds to step 1035 todetermine if the last channel has been scanned. If so, control returnsto the MSU_MAIN sequence 1100 as the MSU 1 is not able to go off hook asall channels are busy. If not, control returns to step 1022 to continuescanning for a vacant channel.

If a channel was vacant, control will have proceeded to the AG-SCANsequence 1026 (FIG. 10C). The sequence commences at step 1040 todetermine if the OFF_HOOK signal is still asserted. If not, controlreturns to the MSU_MAIN sequence 1100. If it is still asserted, controlproceeds to step 1042 where the transmitter 416 is enabled by turning onthe VCC_TX_EN, TX_RF_EN and TX_PLL_EN signals. Control then proceeds tostep 1044, where the ˜AUDIO_EN signal is asserted so that the AUDIO_RXsignal and the TXA signal from the modem M are disabled so that themicrocontroller 412 can send an authorization request or AR command tothe BSU 2. After setting the RADIO variable to command mode, themicrocomputer 412 assembles and transmits an authorization requestcommand as detailed below. The command includes the MSU 1 address tobegin the link security measures. The radio state is then placed instandby mode, where the transmitter RF output is disabled using theTX_RF_EN signal, but the receiver 420 is fully active to await anauthorization grant command from the BSU 2. Resend timer and resendcounter values are cleared to allow a time out function. Controlproceeds from step 1044 to step 1046 to determine if an authorizationgrant command is present in the serial control interface. As noted belowthere are two authorization grants, low power and high power. Low poweris preferred because in the high power mode the power is such that othersystems in more remote locations will not be able to use the samechannel as the higher power signal will have a larger effective servicearea, thus reducing capabilities of the overall system. If anauthorization grant command was not present, control proceeds to step1048 to determine if the resend timer value has reached a preset level.If not, control returns to step 1046. If so, control proceeds to step1050 where the resend counter is incremented. Control then proceeds tostep 1052 to determine if the modem OFF_HOOK signal is still asserted.If not, control returns to the MSU_MAIN sequence 1100. If the modemOFF_HOOK signal is still asserted, this is an indication that there mayhave been a potential clash between MSUs, so control proceeds to step1054 where a random delay period is executed. Each MSU 1 has a uniqueaddress or identifier and this delay period is preferably based on thataddress. This is to allow resolution of potential collision situations.Control then proceeds from step 1054 to step 1044 where theauthorization request is retried.

If a low power authorization grant signal is received in step 1046,control proceeds to step 1056 to determine if the MSU address providedby the BSU 2 in the authorization grant low command matches the MSU 1address present in the MSU 1. In this manner the MSU 1 will not act on agrant command for another MSU 1. If it does not match, control proceedsto the CHANGE_CH sequence 1036. If the addresses match, control proceedsto step 1058 where the radio state is again set to command mode, withthe transmitter 418 turned on, and a GO_OFF_HOOK command is sent fromthe MSU 1 to the BSU 2. The command includes the addresses of both theMSU 1 and the BSU 2 granting authorization to prevent inadvertent offhook activation. Control then proceeds to the MSU_CONN sequence 1060.

If an AGH or authorization grant high power command was received in step1046, control proceeds to step 1062 to determine if the returned MSUaddress matches. If not, control proceeds to the CHANGE_CH sequence1036. If it does match, control proceeds to step 1064 where the resendtimer is cleared and to step 1066 where the BSU address is stored.Control then proceeds to step 1068 to determine if the resend time hastimed out. If not, control proceeds to step 1070 to determine if anauthorization grant low command is also present in the serial controlinterface. If not, control proceeds to step 1068. This loop is usedbecause it has been determined preferable to use a low power BSU if oneis available prior to utilizing a high power BSU. If an AGL command ispresent in step 1070, control proceeds to step 1056. If the resend timehas completed and only an authorization grant high power command hasbeen received, control proceeds from step 1068 to step 1072 where theradio state is again placed in command mode and the ˜AUDIO_EN signalnegated and the GO_OFF_HOOK command is transmitted to the BSU 2providing the high power authorization grant. Control then proceeds tothe MSU_CONN sequence 1060.

The MSU_CONN sequence 1060 (FIG. 10D) initiates at step 1080 where achannel open timer is cleared and set to a value of 15 msec. Controlthen proceeds to step 1082 to determine if the RSSI signal is asserted.If not, control proceeds to step 1084 to determine if the OFF_HOOKsignal is still asserted. If not, control returns to the MSU_MAINsequence 1100. If so, control proceeds to step 1086 where a GO_OFF_HOOKcommand is again provided. This is an attempt to get the BSU 2 activeagain as RSSI should have been asserted but apparently has been dropped.If the RSSI signal was asserted in step 1082, control proceeds to step1088 to determine if the channel open time has completed. If not,control returns to step 1082 to make sure the channel is not dropped andthat the OFF_HOOK command was thus recognized. If the channel open timedoes complete, control proceeds to step 1090 where the radio state isset to modem, which essentially means that the receiver 420 andtransmitter 418 are both active and the ˜AUDIO_EN signal is asserted, sothat the RX and TX analog modem data can be provided through the MSU 1.Control then proceeds to step 1092 to determine if the OFF_HOOK signalnegated. Control loops at step 1092 as long as the modem M is indicatingan off hook state is desired. As soon as the OFF_HOOK signal is negated,indicating the call is to terminate, control proceeds to the MSU_MAINsequence 1100 where the transmitter 416 is turned off, thus dropping theconnection.

The MSU_RING sequence 1014 (FIG. 10E) commences at step 1102 todetermine if the MSU 1 address provided in the ring indication commandis equal to this units address. If not, control returns to the MSU_MAINsequence 1100 as the ring indication was intended for another MSU 1. Ifthe addresses match, control proceeds to step 1104 where the transmitter416 is enabled and a ring timer is cleared. Control then proceeds tostep 1106 where the radio state is placed in command mode, that is the˜AUDIO_EN signal is disabled with the transmitter 416 enabled, and aring acknowledge command is transmitted from the MSU 1 to the base unitBSU 2. The ring acknowledge command includes the BSU 2 and MSU 1addresses for conflict resolution and security. Additionally the RIsignal to the modem M is negated and a resend timer is initialized.Control then proceeds to step 1108 to determine if the RSSI signal isasserted, indicating that a carrier is still present. If not, controlproceeds to step 1110 to determine if the resend timer has completed. Ifnot, control returns to step 1108. If so, control proceeds to step 1112to determine if the ring timer has completed. If not, control returns tostep 1106 to retry the ring acknowledge command. If the ring timer hascompleted, control proceeds to the MSU_MAIN sequence 1100 as the ringingis apparently stopped as the BSU 2 is not responding.

If the RSSI signal is asserted, in step 1108 control proceeds to step1114 where the channel open timer is set. Control proceeds to step 1116to determine if it has timed out yet. If not, control proceeds to step1118 to determine if the RSSI signal is still asserted. If not, controlreturns to step 1108. If it is still asserted, control returns to step1116. Once the channel open time value has been reached in step 1116,control proceeds to step 1120 where a ring on timer is cleared and theRI signal to the modem M is asserted to indicate a ring indication.Control proceeds to step 1122 to determine if the ring on timer valuehas completed. If not, control proceeds to step 1124 to determine if theOFF_HOOK signal has been asserted by the modem M. If not, controlreturns to step 1122. If OFF_HOOK had been asserted, control proceeds tostep 1126 where the GO_OFF_HOOK command is transmitted to the basestation BSU 2 and then the MSU 1 is converted to modem operation, wherethe AUDIO_EN signal is asserted to allow the analog RX and TX to betransmitted. Control then proceeds to step 1128 to determine if theOFF_HOOK signal is asserted. If yes, control loops at step 1128. As soonas the OFF_HOOK signal is negated, control proceeds to the MSU_MAINsequence 1100 to terminate the link.

If the ring on time had completed in step 1122, control proceeds to step1130 where the mode is set to ring off, the RI signal is negated and aring off timer is set. Control then proceeds to step 1132 to determineif the ring off time has completed. If not, control proceeds to step1134 to determine if the OFF_HOOK signal is asserted. If not, controlloops back to step 1132, and if so, control proceeds to step 1126. Ifthe ring off time has completed, control proceeds to step 1136 todetermine if the ring time has completed. If not, control loops back tostep 1120. If so, control proceeds to the MSU_MAIN sequence 1100. Thusthe ring signal is asserted to the modem M for a period of time equal tothe ring on time and then is negated for a period equal to the ring offtime. If at any time during the ringing sequence the OFF_HOOK signal isasserted, indicating that the modem M in the computer C has recognizedthe ring request, control proceeds and the link is established for datatransfer. Otherwise the computer C is considered non-responsive.Preferably the ring on time is 2 seconds, the ring off time is 4 secondsand the total ring time is 20 seconds.

Thus, the MSU 1 monitors for either an off hook indication or a ringindication to become active to either receive data from or transmit datato the appropriate BSU 2.

FIGS. 11A-11E illustrate the operation of the BSU 2. The boot sequence1180 commences at step 1182 where the various ports and program tablesare initialized and the serial control interface is turned on.Additionally, the radio, i.e. the transmitter/receiver pair, is set toan off state. Control proceeds to step 1184, which is the entry point ofthe BSU_MAIN sequence 1200. At step 1184 the serial control interface isdisabled and the radio system is again placed in an off mode, where boththe transmitter 426 and receiver 428 are disabled and powered down, anda ring counter and a wait timer are both cleared. Control proceeds tostep 1186 where the serial control interface is once again disabled andthe internal timer in the microcomputer 430 is set to interruptoperation upon overflow. Following this, the WAIT instruction of themicrocomputer 430 is executed so that the system goes into a low poweron mode. In this case both the transmitter 426 and the receiver 428 arepowered off and the microcontroller 430 has entered a low power downmode, thus minimizing the power consumption of the BSU 2 to conserve thecharge in the capacitor in the power supply 434.

After the timer period of approximately 5 seconds is completed, themicrocomputer 430 wakes up and control proceeds to step 1190 where theserial control interface is enabled so that any signal received from theMSU 1 can be received. Control proceeds to step 1192 to determine if theBSU 2 is off hook. If so, control proceeds to step 1194 to determine ifat least one ring has been received. If so, control proceeds to aBSU_CCA sequence 1196. If no rings have been received or the OFF_HOOKsignal was not asserted, control proceeds from steps 1192 and 1194 tostep 1198 to determine if a ring has been received and the BSU 2 has anactive MSU address of other than zero. If it is zero, this indicatesthat no MSU 1 is designated to receive the call and therefore answeringis not appropriate. Addresses are designated either by being the lastMSU to use the BSU 2 or by a special configuration command as discussedbelow. If an address is designated, control proceeds to step 1202 wherethe ring indication count is incremented and then control proceeds tostep 1204 to determine if the ring count value is greater than or equalto 2. If so, control returns to step 1186 because it is determined thatit is appropriate to pick up only the first ring. This condition isreached only if the MSU 1 is not responding to the ring indication. Ifthe ring count is less than 2, that is it is 1, control proceeds to theBSU_CCA sequence 1196. If in step 1198 it was determined that the activeMSU address was zero or there was no ring indication, control proceedsto step 1206 where the ring indication counter is cleared and then tostep 1208 to determine if the wait time has completed. If not, controlreturns to step 1186. If so, control proceeds to step 1210 where thereceiver 428 is activated so that the radio is placed in listening mode.This is done by powering up the receiver 428 and enabling it. Controlthen proceeds to the BSU_AUTH sequence 1212.

The BSU_AUTH sequence 1212 commences at step 1214 where a dwell timer iscleared. Control then proceeds to step 1216 to determine if anauthorization request or GO_OFF_HOOK command has been received in theserial control interface. If not, control proceeds to step 1218 todetermine if the dwell timer has completed. If not, control returns tostep 1216. If so, control proceeds to the BSU_CGCH sequence 1220.Preferably the dwell time is 250 msec so that during this dwell periodthe BSU 2 looks for commands from the MSU 1. If none are received, thechannel is changed and the BSU 2 goes back to wait mode. Thus the BSU 2sleeps for a period, and awakens briefly to look for a ring and thenreturns to sleep. After a number of these cycles the BSU 2 brieflymonitors for MSU 1 activity and then returns back to sleep.

If in step 1216 it was determined that a GO_OFF_HOOK command wasreceived, control proceeds to step 1222 to determine if the addressprovided by the MSU 1 is in the response authorization table, the listof MSUs to which the BSU 2 is authorized to respond. If not, controlproceeds to the BSU_CGCH sequence 1220. If it is authorized, controlproceeds to step 1224 to determine if the MSU address provided in theGO_OFF_HOOK command matches that provided in the ring indicationacknowledge command or the authorization request command. If not,control proceeds to step 1227, where the radio is placed in the listenmode so the transmitter 426 is disabled and only the receiver 428 isenabled, and then control proceeds to the BSU_CGCH sequence 1220. If theMSU address is matched, control proceeds to step 1226 where the radio isplaced in the modem mode, that is, the audio is enabled and thetransmitter 426 and receiver 428 are both fully active, and then controlproceeds to the BSU_DISC sequence 1228. It is noted that a separateoperation to go off hook is not required as the BSU 2 goes off hookevery time the transmitter 426 is enabled, as described above.

If in step 1216 it was determined that the authorization request commandwas received, control proceeds to step 1230 to determine if the addressof the MSU 1 is in the authorization table. If not, control loops backto step 1216. In this manner, a user simply cannot obtain access to aBSU 2 if the MSU 1 has not been authorized or qualified. This preventsusers from simply walking to a third party base station BSU and makingcalls using a different MSU. This limits inadvertent toll charges andaccess of information. If the MSU 1 was authorized, control proceeds tostep 1232 where the transmitter 426 enabled but the system is placed ina standby mode, with both the transmitter 426 and the receiver 428enabled, but with the transmit RF output disabled by use of the TX_RF_ENsignal. Further, the resend count is cleared. Control proceeds to step1234 where the radio is placed in command mode with the audio disabledand the RF output enabled and the authorization grant low command istransmitted to the mobile station MSU 1 requesting a channel. The radiois then placed in standby mode pending a response. Further, the resendtimer is cleared. Control then proceeds to step 1236 to determine if theGO_OFF_HOOK command has been received from the MSU 1. If not, controlproceeds to step 1238 to determine if the resend time value hascompleted. If not, control returns to step 1236 awaiting the commandfrom the MSU 1. If the resend time value has completed, control proceedsto step 1240 where the resend count value is incremented. Controlproceeds to step 1242 to determine if the resend count value is lessthan or equal to a predetermined value. If so, control proceeds to step1244, which is a delay for a random period based on the station address.This is utilized in the case of a potential collision between two MSUs.Control then proceeds to step 1234 to retry the authorization grantcommand. If the resend count value has exceeded the predetermined limit,control proceeds to step 1246 where the radio is placed in the listenmode, that is, the transmitter 426 is disabled, and then controlproceeds to the BSU_CGCH sequence 1220.

The BSU_CGCH sequence 1220 (FIG. 11C) commences at step 1260 where theserial control interface is disabled and the channel number isincremented to test another channel. Control then proceeds to step 1260to determine if the last channel has been utilized. If so, controlproceeds to the BSU_MAIN sequence 1200. If not, the receiver 428 isenabled so that the radio is in listen mode and the serial controlinterface is activated in step 1264. Control then proceeds to theBSU_AUTH sequence 1212 to scan the other channel.

The BSU_DISC sequence 1228 commences at step 1270 where a channel vacanttimer is cleared. Control proceeds to step 1272 to determine if the RSSIsignal is asserted. This would be an indication that an MSU 1 isattempting communication on that channel. If so, control returns to step1270. If not, control proceeds to step 1274 to determine if the channelvacant time has completed. If not, control returns to step 1274 so thatthe BSU 2 remains inactive for at least the minimum time required toindicate that the channel is vacant. If the channel vacant time hascompleted, control proceeds to the BSU_MAIN sequence 1200. This is howthe BSU 2 indicates that a particular channel is available for operationagain.

The BSU_CCA sequence 1196 (FIG. 11D) commences at step 1300 where thechannel vacant timer is cleared. Control proceeds to step 1302 todetermine if the RSSI signal is asserted. If not, control proceeds tostep 1304 to determine if the channel vacant time has completed. If not,control loops back to step 1302. If so, control proceeds to the BSU_RINGsequence 1306 where a ring indication is sent to the MSUs. If the RSSIsignal is asserted, indicating that the channel is not vacant, controlproceeds to step 1305 where the channel open timer is set. Control thenproceeds to step 1307 to determine if the RSSI signal is asserted. Ifnot, control returns to step 1302 awaiting a channel as it would havejust opened. If the RSSI signal is still asserted, control proceeds tostep 1308 to determine if the channel open time is completed. If not,control returns to step 1307. If so, this is an indication that thechannel is occupied. Control then proceeds to step 1310 where thechannel number is incremented. Control proceeds to step 1312 todetermine if this is the last channel. If so, control returns to theBSU_MAIN sequence 1200 and the call will not be answered. If this is notthe last channel, control proceeds from step 1312 to step 1300 where thenext channel is then scanned for operation.

The BSU_RING sequence 1306 commences operation at step 1320 where thetransmitter 426 is enabled and the ring timer is cleared. Control thenproceeds to step 1322, where the radio is placed in command mode so thata command can be transmitted and then the ring indication command istransmitted from the BSU 2 to the MSU 1. The radio is then placed instandby mode awaiting a response and the resend timer and resend countvalues are cleared. Control proceeds to step 1324 to determine if a ringindication acknowledge command has been received from the MSU 1. If not,control proceeds to step 1326 to determine if the resend time value hascompleted. If not, control loops back to step 1324. If it has completed,control proceeds to step 1328 to increment the resend count. Controlthen proceeds to step 1330 to determine if the ring time value hascompleted. If not, control proceeds to step 1332 where a random delay isprovided and then control returns to step 1322. If the ring time iscompleted, indicating that the ring sequence is over and has not beenacknowledged, control proceeds to the BSU_MAIN sequence 1200.

If the ring acknowledge command was received, control proceeds from step1324 to step 1332 to determine if the BSU address as provided in thering indication acknowledge command is the same as that of theparticular BSU 2. If not, control proceeds to step 1334 where thechannel value is incremented and then to step 1336 to determine if thiswas the last channel. If not the last channel, control returns to step1322. If the last channel, control proceeds to the BUS_MAIN sequence1200 as a channel is not available to provide a secure link. If the BSUaddress does match in step 1332, control proceeds to step 1338 where theradio is placed in command mode. Control then proceeds to step 1340 todetermine if a GO_OFF_HOOK command has been received. If not, controlproceeds to step 1342 to determine if the ring time has been completed.If not, control loops to step 1340. If the ring time has completed,indicating that the ring indication acknowledge has been received butthe off hook command has not been received in a sufficient period,control proceeds to the BSU_MAIN sequence 1200 so that the call is notaccepted. If the GO_OFF_HOOK command has been received, control proceedsfrom step 1340 to step 1344 where the receiver 428 and transmitter 426are placed in modem mode so that the analog TX or RX data is transmittedcorrectly. Control then proceeds to the BSU_DISC sequence 1228 to waitfor loss of the channel signal from the MSU 1 to drop the link. The MSU1 holds open the activity of the base station BSU 2 by providing acontinuous carrier signal.

In this description it has been assumed that a full command is providedor received by the serial control interface. However, as a command is 6or 9 bytes long, multiple operations are actually required to develop orsend a full command. The serial control interface provides an interrupton receipt or transmission of a data byte. A software routine is used toassemble a received command and do any required checksum operation andto breakdown a transmitted command and provide the checksum. Thisroutine has been omitted for simplicity and can be readily developed byone skilled in the art.

Detailed operations on loading of authorization addresses into the BSU 2are not described to simplify the description. This authorization ispreferably done utilizing special command software which is availablefrom the manufacturer. Preferably the units will be shipped from themanufacturer with each unit authorized to talk to each other. If furtheraddresses must be authorized, as will be common in a businessenvironment, then the command software will be utilized. Preferably thecommand operation utilizes the DTMF encoders/decoders to capture aspecific telephone number provided over a DTMF channel, such as a 555number not otherwise utilized for communications. This number is sensedby the microcomputer 430 in the BSU 2 and then the address of the BSUbeing programmed and the particular MSU to be authorized are provided,preferably also using DTMF signalling. Then BSU 2 then loads thisinformation into the authorization table. Other techniques for enteringthis could be readily developed, such as a serial port attachment. It isnoted that these commands are not necessary for normal operation oncethe units are authorized, so that after the initial set up of the unitsby and individual user the operation is transparent to thecommunications software.

It is also noted that other command signaling techniques could beutilized. For example, DTMF signalling could be used instead of FSKsignalling. In this case the microcontroller will provide or receiveeach character to the DTMF encoder/decoder. Otherwise command operationwould be similar.

Therefore several factors can be seen. One is that the operation of thelink is entirely transparent to any communication software operating onthe computer as the cordless system operates based only on the hardwaresignals provided by the output of the modem M and the signals on thetelephone line. A user is thus able to use his existing communicationsoftware package without changing any regard. No special commandlanguage has to be developed for normal operations of the link. It canalso be seen that there is checking of the availability of a channel andfrequent checking of addresses prior to actually developing ownership ofa specific channel. As can be seen in the table below, each of thecommands includes the appropriate station addresses to allow a fullychecked and authorized operation to be developed. A plurality of MSUscan be present and talk to a plurality of BSUs but only one MSU isavailable to utilize a single BSU at a time for a single event and noother MSU is capable of utilizing that same BSU or eavesdropping fromthe communications process from the MSU to the BSU during the operation.Further, the use of two channels allows multiple units to exist in asmaller area without potential overlap or unavailability.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape, materials, components, circuit elements, wiring connections andcontacts, as well as in the details of the illustrated circuitry andconstruction and method of operation may be made without departing fromthe spirit of the invention.

What is claimed is:
 1. A transmitting system for transmitting modem databetween a computer and a telephone line of a telephone system, thetransmitting system comprising: a modem coupled to the computer; thecomputer for providing modem commands to the modem; a mobile unitconnected to the modem, said mobile unit having a mobile unitidentification value and including: a modem interface coupled to themodem for receiving the modem data and dialing signals from the modemand for providing the modem data to the modem; a mobile unit radiofrequency transceiver connected to said modem interface for transmittingthe modem data and the dialing signals over a radio frequency channeland for receiving the modem data over the radio frequency channel;mobile unit command processor coupled to said mobile unit radiofrequency transceiver for providing and receiving command informationover the radio frequency channel; and mobile unit operations controllercoupled to said mobile unit command processor for performing operationsresponsive to the command information received by said mobile unitcommand processor; and a base unit connected to the telephone line, saidbase unit having a base unit identification value and including: a dataaccess arrangement for receiving the modem data from and providing themodem data and the dialing signals to the telephone line, wherein thedata access arrangement is directly coupled to the telephone line; abase unit radio frequency transceiver coupled to said data accessarrangement for transmitting the modem data over the radio frequencychannel and for receiving the modem data and the dialing signals overthe radio frequency channel, said base unit radio frequency transceiveroperating with said mobile unit radio frequency transceiver; base unitcommand processor coupled to said base unit radio frequency transceiverfor providing and receiving the command information over the radiofrequency channel; and base unit operations controller coupled to saidbase unit command processor for performing operations responsive to thecommand information received, wherein the command information providedby said mobile unit command processor and said base unit commandprocessor includes said mobile unit identification value and said baseunit identification value, wherein said mobile unit operationscontroller operates only if the command information received includesthe mobile unit identification value of said mobile unit, and whereinduring communication between said mobile unit and said base unit, saidmobile unit transmits the base unit identification value of said baseunit so that only said base unit communicates with said mobile unit. 2.The transmitting system of claim 1, further comprising: a wireless datalink for communicating the modem data between said modem unit radiofrequency transceiver and said base unit radio frequency transceiver. 3.The transmitting system of claim 1, wherein said mobile unit isintegrated with the modem into a single unit.
 4. The transmitting systemof claim 1, said base unit being connected to the telephone line througha phone jack, wherein said mobile unit is located away from the phonejack.
 5. The transmitting system of claim 1, wherein the radio frequencychannel includes a transmit channel and a receive channel.
 6. Thetransmitting system of claim 5, wherein the transmit channel operates ata center frequency of 35.2 MHZ and the receive channel operates at acenter frequency of 42.24 MHZ.
 7. A transmitting system for transmittingmodem data between a computer and a telephone line of a telephonesystem, the transmitting system comprising: modem coupled to thecomputer, said modem adapted for connection to a Public TelephoneNetwork; the computer for providing modem commands to the modem; amobile unit connected to the modem, said mobile unit having a mobileunit identification value and including: a modem interface coupled tothe mode for receiving the modem data and dialing signals from the modemand for providing the modem data to the modem; a mobile unit radiofrequency transceiver connected to said modem interface for transmittingthe modem data and the dialing signals over a radio frequency channeland for receiving the modem data over the radio frequency channel;mobile unit command processor coupled to said mobile unit radiofrequency transceiver for providing and receiving command informationover the radio frequency channel; and mobile unit operations controllercoupled to said mobile unit command processor for performing operationsresponsive to the command information received by said mobile unitcommand processor; and a base unit connected to the telephone line, saidbase unit having a base unit identification value and including: a dataaccess arrangement for receiving the modem data from and providing themodem data and the dialing signals to the telephone line, wherein thedata access arrangement is directly coupled to the telephone line; abase unit radio frequency transceiver coupled to said data accessarrangement for transmitting the modem data over the radio frequencychannel and for receiving the modem data and the dialing signals overthe radio frequency channel, said base unit radio frequency transceiveroperating with said mobile unit radio frequency transceiver; base unitcommand processor coupled to said base unit radio frequency transceiverfor providing and receiving the command information over the radiofrequency channel; and base unit operations controller coupled to saidbase unit command processor for performing operations responsive to thecommand information received, wherein the command information providedby said mobile unit command processor and said base unit commandprocessor includes said mobile unit identification value and said baseunit identification value, wherein said mobile unit operationscontroller operates only if the command information received includesthe mobile unit identification value of said mobile unit, wherein duringcommunication between said mobile unit and said base unit, said mobileunit transmits the base unit identification value of said base unit sothat only said base unit communicates with said mobile unit; and whereincommunication between said mobile unit and said base unit over saidradio frequency channel is a one-to-one dedicated transmission.
 8. Thetransmitting system of claim 7, further comprising: a wireless data linkfor communicating the modem data between said modem unit radio frequencytransceiver and said base unit radio frequency transceiver.
 9. Thetransmitting system of claim 7, wherein said mobile unit is integratedwith the modem into a single unit.
 10. The transmitting system of claim7, said base unit being connected to the telephone line through a phonejack, wherein said mobile unit is located away from the phone jack. 11.The transmitting system of claim 7, wherein the radio frequency channelincludes a transmit channel and a receive channel.
 12. The transmittingsystem of claim 11, wherein the transmit channel operates at a centerfrequency of 35.2 MHZ and the receive channel operates at a centerfrequency of 42.24 MHZ.
 13. A transmitting system for transmitting modemdata between a computer and a telephone line of a telephone system, thetransmitting system comprising: a modem coupled to the computer, saidmodem adapted for connection to a Public Switched Telephone Network; thecomputer for providing modem commands to the modem; a mobile unitconnected to the modem, said mobile unit having a mobile unitidentification value and including: a modem interface coupled to themodem for receiving the modem data and dialing signals from the modemand for providing the modem data to the modem; a mobile unit radiofrequency transceiver connected to said modem interface for transmittingthe modem data and the dialing signals over a radio frequency channeland for receiving the modem data over the radio frequency channel;mobile unit command processor coupled to said mobile unit radiofrequency transceiver for providing and receiving command informationover the radio frequency channel; and mobile unit operations controllercoupled to said mobile unit command processor for performing operationsresponsive to the command information received by said mobile unitcommand processor; and a base unit connected to the telephone line, saidbase unit having a base unit identification value and including: a dataaccess arrangement for receiving the modem data from and providing themodem data and the dialing signals to the telephone line, wherein thedata access arrangement is directly coupled to the telephone line; abase unit radio frequency transceiver coupled to said data accessarrangement for transmitting the modem data over the radio frequencychannel and for receiving the modem data and the dialing signals overthe radio frequency channel, said base unit radio frequency transceiveroperating with said mobile unit radio frequency transceiver; base unitcommand processor coupled to said base unit radio frequency transceiverfor providing and receiving the command information over the radiofrequency channel; and base unit operations controller coupled to saidbase unit command processor for performing operations responsive to thecommand information received, wherein the command information providedby said mobile unit command processor and said base unit commandprocessor includes said mobile unit identification value and said baseunit identification value, wherein said mobile unit operationscontroller operates only if the command information received includesthe mobile unit identification value of said mobile unit, and whereinduring communication between said mobile unit and said base unit, saidmobile unit transmits the base unit identification value of said baseunit so that only said base unit communicates with said mobile unit. 14.The transmitting system of claim 13, further comprising: a wireless datalink for communicating the modem data between said modem unit radiofrequency transceiver and said base unit radio frequency transceiver.15. The transmitting system of claim 13, wherein said mobile unit isintegrated with the modem into a single unit.
 16. The transmittingsystem of claim 13, said base unit being connected to the telephone linethrough a phone jack, wherein said mobile unit is located away from thephone jack.
 17. The transmitting system of claim 13, wherein the radiofrequency channel includes a transmit channel and a receive channel. 18.The transmitting system of claim 17, wherein the transmit channeloperates at a center frequency of 35.2 MHZ and the receive channeloperates at a center frequency of 42.24 MHZ.